1. Field of the Invention
The present invention relates to a semiconductor device including an oxide semiconductor and a manufacturing method thereof.
Note that semiconductor devices in this specification mean all devices which can function by utilizing semiconductor characteristics, and electro-optical devices such as display devices, semiconductor circuits, and electronic devices are all semiconductor devices.
2. Description of the Related Art
In recent years, a technique by which a thin film transistor (TFT) is manufactured using a semiconductor thin film (having a thickness of approximately several nanometers to several hundred nanometers) formed over a substrate having an insulating surface has attracted attention. Thin film transistors have been applied to a wide range of electronic devices such as ICs or electro-optical devices and urgently developed particularly as switching elements in image display devices. Various metal oxides are used for a variety of applications. For example, indium oxide is a well-known material and has been used as a transparent electrode material which is necessary for liquid crystal display devices or the like.
Some metal oxides exhibit semiconductor characteristics. The examples of such metal oxides having semiconductor characteristics are a tungsten oxide, a tin oxide, an indium oxide, a zinc oxide, and the like. A thin film transistor in which a channel formation region is formed using such metal oxides having semiconductor characteristics is known (Patent Document 1 and Patent Document 2).